The invention relates to the art of spectrum-shaping or filtering of noisy signals.
The utilization of speech signals, data translation links, communication nets and the like is of times hampered or limited due to the unavoidable presence or injection otherwise of noise and interfering signals. In the receiver process or video detection of noisy RF signals, the video process and associated video circuit delays tend to integrate the presence of such noise. A usual method of obtaining spectral shaping or "filtering" has been the performance of spectrum-whitening by means of the classical predictive-deconvolution filters, as described by B. Widrow et al in the article "Adaptive Noise Cancelling; Principles and Applications", Proc. IEEE, Vol. 63, pages 1692-1716, Dec. 1975. If a spectrum shape other than flat is desired, then the deconvolution filter is usually followed by a second filter whose frequency response matches the shape of the desired spectrum, as described by J. E. Paul in the paper "Adaptive Digital Techniques for Audio Noise Cancellation", Proc. 1978 ISCAS (International Symposium for Circuits and Systems), New York, May 1978 (sponsored by IEEE). Many signal-processing problems, such as the restoration of natural-sounding spectrum to computer-enhanced speech, are amenable to such solution of sequentially spectrum-whitening and then spectral-shaping. However, in noisy signal-processing applications, involving detection of, say, a specific spectral line contained amid a very rich spectrum the above-described method may be inadequate, for the reason that the spectrum whitening procedure discriminates against the sought-after signal as much as any other component of the spectral content. In other words, in flattening and attenuating the spectrum, the spectral line of interest is similarly attenuated.